Printing telegraph signal normalizer



E. N. DINGLEY, JR

HUNTING TELEGRAPH SIGNAL NORMALIZER Oct. 18, 1955 Filed Oct. 2, 1953 m55 20:02am

United States Patent O PRINTING TELEGRAPH SIGNAL NORMALIZER Edward Nelson Dingley, Jr., Arlington, Va.

Application October 2, 1953, Serial No. 383,761

9 Claims. (Cl. 178-53.1)

My invention relates broadly to means for normalizing printing telegraph signals, that is, to means for converting printing telegraph signals that are characterised by an irregular character rate into signals having identical symbolage and a constant character rate equal to the time average of the irregular rate.

My invention relates chiefly to means by which printing telegraph signals delivered by a communication link at an irregular character rate may be converted to a constant character rate equal to the time-average of the irregular rate, and means for correcting the speed of a receiving printing telegraph equipment to synchrony with the aforesaid average character rate.

One of the objects of my invention is to provide a device that will permit the satisfactory linking of transmitting and receiving time-synchronous printing telegraph apparatus through any channel of the military type AN/FGC-S time-division multiplex equipment or through any similar multiplex equipment.

Another object of my invention is to provide a device that will permit the satisfactory linking of transmitting and receiving time-synchronous 7.0 unit printing telegraph apparatus through a communication link containing regenerative repeaters the nature of which is to convert 7.0 unit characters into 7.42 unit characters.

Other and further objects of my invention will be understood from the following specication and by reference to the accompanying drawing in which:

Fig. l diagrammatically illustrates one embodiment of my invention.

Fig. 2 is a sectional View of cam 29 as seen along the line A-A in Fig. l.

Fig. 3 is a sectional view of cam 43 as seen along line B-B in Fig. 1.

Fig. 4 is a sectional view of cam 38 as seen along line C-C in Fig. l.

In certain applications of printing telegraph apparatus (hereafter abbreviated to PTA), the use of conventional start-stop type PTA is unsatisfactory because the noise and fading conditions encountered on certain communication links frequently suppress start signals originated at the transmitting terminal and in consequence, the receiving PTA will omit a complete character without warning that a character has been omitted, thus introducing the possibility of completely changing the intelligence content of a message (i. e., correspondent changed to corespondent) To overcome this diiculty, time-synchronous printing telegraph apparatus (of which the Teletype Corporations Monoplex is one example) has been developed. In such apparatus, the time rate at which characters are transmitted is constant and the receiving apparatus, which runs synchronously under the control of a local timestandard, introduces a locally-generated start pulse at the correct instant whenever a start pulse is suppressed by the communication link. The rate of the local time standard is corrected against drifting by sampling the average rate at which characters are received.

The type AN/FGC-S multiplex apparatus (hereinafter abbreviated to mux) is designed to operate in conjunction with start-stop PTA and in a manner such as to obviate the necessity for synchronizing the PTA to the mux. This is accomplished by selecting a mux character rate (per channel) slightly greater than the normal maximum character rate of the transmitting PTA; by providing each input-channel of the transmitting mux with buffer-storage stages capable of storing PTA characters pending the correct instant for transmission in the multiplex cycle; by providing means for recognizing the condition wherein no character is in storage for transmission by reason of the fact that the mux character-rate exceeds the PTA character-rate; by providing means under such conditions for transmitting a time-diiferential blank character during such multiplex cycle; and by providing means at the receiving mux terminal to recognize and suppress from the output channel such timediiferential blanks.

The signals delivered by an output channel of a receiving type AN/FGC-S .mux consist of a spacing-start baud of one-unit duration followed by tive one-unit duration intelligence bauds (either marking or spacing) followed by a marking-stop baud of approximately 1.42 units duration; thus the duration of each character is 7.42 time units=T2 milliseconds. lf, for example, the duration of each character delivered to the transmitting mux by the transmitting PTA is T1 milliseconds (by reason of the slower character rate of the transmitting PTA), the transmitting mux will advance Ti-T 2 milliseconds in time phase, with respect to the transmitting PTA, every T2 milliseconds. At the end of N such T2 millisecond periods, the phase advance will be N (T1-T 2) milliseconds or nearly one full mux character period and there will be no character in buffer-storage of the transmitting mux. This causes the transmitting mux to transmit, in one mux character time interval (T2 milliseconds), a time-differential blank which the receiving mux converts into a marking-stop signal of T2 milliseconds duration. If the receiving PTA is of the start-stop type intended for use with the AN/FGC-S mux, and if noise and fading on the communication link never deletes a start pulse, the receiving PTA will print a character each T2 milliseconds for a sequence of N characters and then cease operation during the next succeeding T2 milliseconds.

lf, under the conditions described above, noise and fading on the communication link do delete an occasional start pulse, occasional valid characters will be omitted from the received message and the communication system will not be satisfactory. To overcome this unsatisfactory condition, it would be desirable to make the receiving PTA synchronous with the transmitting PTA in order that some character, even a garbled character, is received for each character transmitted. However, a receiving PTA running synchronously with the transmitting PTA at a constant rate cannot accept characters delivered by the mux at a variable rate nor can the timestandard of the synchronous receiving PTA be corrected, when necessary, by characters delivered at a variable rate.

My invention, the printing telegraph signal normalizer, is capable of receiving and temporarily storing the signals delivered at a variable character rate by the output of the mux, and is capable of normalizing and delivering these signals to a synchronous receiving PTA at the same constant character rate that they are transmitted by the synchronous transmitting PTA. My invention additionally is capable of sensing small diiferences between the rate of the transmitting PTA and the rate of the receiving PTA and of correcting the rate of the latter so as to minimize such dilferences.

One embodiment of my invention is illustrated diagrammatically in Fig. l wherein input line relay 2 is energized by incoming start-stop printing telegraph signals delivered by an output channel of a receiving type AN/FG'C-S multiplex equipment; wherein a signal-distributor D2, driven intermittently through clutch ii" and reduction gear'2d by motor M2, distributes in accordance with standard teletypewriter practice, the incoming signals through the intervention of 5-pole switching relay le, in such a manner that the intelligence bauds of odd-xu. bered received characters are stored in storage relays through 25, and even-numbered characters are stored .in storage relays 8l through 85, the alternate character storage being accomplished by energizing terminal i of switching relay 16 by the closure of cam-switch Fs (see section A-A) during odd-numbered revolutions of distributor D2 and by cle-energizing relay if by the opening of cam-switch F5 during the even-numbered revolutions of distributor D2, the alternate operation of cam-switch F5 being accomplished by gearing cam 29 to shaft l@ through the 2-1 reduction gears 27 and 2S; wherein a signal-distributor D1, driven by shaft 37 in synchrony with the receiving PTA, distributes the signals stored in relays 21 through 25 and the signals stored in relays 8l through SS in alternate order to output line relay 9i) and thence to the receiving PTA, the alternate character distribution being accomplished by energizing terminal Q of S-pole switching relay by the closure of cam-switch F6 (see section C-C) during odd-numbered revolutions of distributor D1 and by de-energizing relay 3d by the opening of cam-switch Fe during the even-numbered revolutions of distributor D1, the alternate operation of camswitch being accomplished by gearing cam 38 to shaft 37 through the Z-l reduction gears 41 and 42; and wherein switches F1 through F4 (see section B-B), operated by cam 43 which is driven through gears d5 and 4d from differential 47, operate in a manner to be described to correct abnormal functioning of the system.

in the following detailed description of one embodiment of my invention as illustrated in Figs. l, 2 and 3, it will be assumed that the first input character to be referred to is that input character whose spacing-start baud commences at the instant that cams 29 and 3S are in the positions illustrated, that is, at the instant that switches F5 and Fs are about to close. It will also be assumed that the time required for distributor D2 to complete a revolution is T2 milliseconds which is also the duration of each printing telegraph character delivered by the mux to input line relay 2. It will also be as that the time required for distributor D1 to comi; revolution is T1 milliseconds which is also the duration of each synchronous PTA character.

The start baud of the first character received by input line relay 2 will be a spacing baud (standard teletypewriter practice) which follows the marking-stop baud the preceding character. This spacing-start baud will de energize relay 2 and engage springs 2A and 2S thus placing ground potential on the lower contacts of switches W1 through W5 (all non-engaged) of distributor D2 and on the magnet of relay 6. Relay 6, being not energized, engages springs 6A and 6B thus energizing clutch magnet 9 from positive battery via terminal T on relay contact did. Energizing clutch magnet 9 engages clutch i7 and thus distributor D2 and cam 29 start to rotate. Within 2 or 3 milliseconds, cam 29 closes switch F5 which energizes switching relay i6 and engages tongues 11A through 15A with springs 1TB through 15B respectively. During this same period of 2 or 3 milliseconds cam 35B has rotated sufficiently to close switch Fs (see section C C) which energizes switching relay 30 and engages tongues 31A through 35A with springs 31B through 35B rcspectively.

The next baud received by the input line relay 2 is the rst intelligence baud of the rst input character, The cams of distributor D2 are phased so as to close contacts W1 during the life or this baud. lf the baud is marking,

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springs 2A and 2C of relay 2 engage and connect battery through contacts W1 of distributor D2, through springs 11A and 11B of relay 16 to the magnet of storage relay 21 thus engaging springs 21A and 21B and also springs 21C and 21D. The closing of springs 21A and ZB places battery on the magnet of relay 21 by way of resistor R1 thus holding relay 21 closed even after contact W1 has opened. If the first intelligence baud of the rst character had been spacing, instead of marking as described above, ground potential would have been applied to relay 21 and it would have remained de-energized. In a similar manner the cams and contacts W2 through W5 of distributor D2 distribute the remaining four marking or spacing intelligence bauds of the irst character to storage relays 22 through 25 respectively. The last baud of the first character received by input relay 2 is a marking-stop baud (standard teletypewriter practice) which energizes relay 6, opens springs 6A and 6B, de-energizes clutch magnet 9, disengages clutch 17, and stops the rotation of distributor D2 at the conclusion of time interval T2. The standard design of teletypewriter clutch 17 is such that marking intelligence bauds do not disengage the clutch or stop distributor D2.

During the foregoing time interval T2, the cams of distributor D1 have been revolving, at such a rate as to complete one revolution in time interval T1, and they close distributor contacts Zo through Ze in sequence so as to create either a 7.42 baud or a 7.0 baud printing telegraph signal as desired. The closing of contact Z0 may apply either ground potential to output line relay 90 to provide the usually-desired spacing-start baud of the irst output character or it may be connected to apply battery to output line relay 90 to provide the marking-start baud required in certain special applications. The closing of contact Z1 connects output line relay 90 through springs 31A and 31B of S-pole switching relay 30 to spring 21D of storage relay 21. lf this relay is locked-up, battery will be contacted through spring 21C and a marking signal will be transmitted by output line relay 90; otherwise a spacing signal will be transmitted. In a similar manner, contacts Z2 through Z5 of distributor D1 closing in sequence, sample the baud information stored in storage relays 22 through 25 and transmit corresponding bauds to output line relay 90. The closing of contact Z6 may apply either battery potential to output line relay 90 to provide the usually desired marking stop baud of the rst output character or it may be connected to apply ground potential to relay 90 to provide the spacing-stop baud required in certain special applications.

The distributor D2 has completed one revolution in T2 milliseconds at which time switch F5 opens thus deenergizing the magnet of relay 16 and engaging tongues HA through 15A with springs 11C through 15C respectively preparatory to the storage of the ve intelligence bauds of the second input character in the storage relays 31 through 85 in the same manner that the five intelligence bauds of the iirst input character were stored in the storage relays 21 through 25.

Since distributor D1 requires T1 milliseconds to complete a revolution, it will have completed only T2/ T1 parts of a revolution when distributor D2 has completed a full revolution in T2 milliseconds and the time-phase of distributor D1 lags behind that of distributor D2 by T1-T2 milliseconds, but distributor D1 is still able to sample the baud information stored in storage relays 2l through 25 because they have not yet changed. At the end of T1 milliseconds, switch Fe de-energizes switching relay 3l) thus engaging tongues 31A through 35A with springs 32C through 35C respectively and permitting contacts Z1 through Z5 to sample the intelligence bauds of the second input character which have been stored in storage relays 81 through 85 as described heretofore.

At the beginning of the third period of T2 milliseconds, distributor D2 Starts to receive the third input character,

switch F energizes switching relay 16 and, one (start) baud interval later, switch W1 closes thus introducing the first intelligence baud of the third character to storage relay 21. If this first said intelligence baud is spacing and the baud previously stored in relay 21 was also spacing, the condition of relay 21 remains spacing. If this first said baud is marking and the baud previously stored in relay 21 was also marking, the condition of relay 21 remains marking. If this first said baud is marking and the baud previously stored was spacing, the battery potential derived through springs 2A and 2C of input line relay 2 will, by way of contacts W1 of distributor D2, energize storage relay 21 which will remain locked-up as previously described even after contacts W1 have opened. If the first said baud is spacing and the baud previously stored in storage relay 21 was marking, ground potential derived through springs 2A and 2B of input line relay 2 will, by way of contacts W1 of distributor D2, short-circuit the magnet of storage relay 21 causing relay 21 to de-energize and to remain de-energized because the holding contacts 21A and 21B have been thus opened. The momentary short circuiting of resistor R1 is harmless.

In a similar manner the remaining marking or spacing intelligence bauds of the third input character are substituted for those of the first input character which were previously stored in storage relays 21 through 25. In a similar manner the intelligence bauds of the succeeding even numbered characters are stored in storage relays 81 through 85 and those of succeeding odd numbered characters are stored in storage relays 21 through 2S.

Distributor D2 will complete its first revolution in T2 milliseconds during which time distributor D1 will complete T z/T 1 parts of a revolution and distributor D2 will lead distributor D1 in space-phase by parts of a revolution. At the conclusion of N1 revolutions of distributor D2, distributor D2 will lead distributor D1 by N1(T1-T 2)/T1 parts of a revolution. The design of the type AN/FGC-5 mux is such that when T2/(T1-T2):Nl-l-Xi/(T1-T2), and N1 characters have been transmitted, the mux transmits a time differential blank because there is no complete character in storage, and the receiving mux translates this time differential blank into a marking-stop signal having a duration of T2 milliseconds. This marking-stop signal causes distributor D2 to remain at rest for a period of T2 milliseconds. In the foregoing equation At the conclusion of N1 characters, distributor D2 will lead distributor D1 by N1(T1-T2)/ T1 parts of a revolution stated above. During the next interval of T2 milliseconds, distributor D2 remains stationary while distributor D1 advances by Tz/ T1 parts of a revolution relative to distributor D2. In consequence, immediately prior to receipt of the next input character, distributor D1 leads distributor D2 by T2/T1-N1(T1T2) /T1 parts of a revolution.

At the conclusion of the receipt of the next N2 quantity of input characters, distributor D2 will lead distributor At the conclusion of N2 characters, the receiving mux will deliver a marking-stop signal of T2 milliseconds parts of a revolution.

This process continues and the lead of distributor D2 over distributor D1 after N1-I-N2-l- Nn characters will be parts of a revolution and the lead of distributor D1 over distributor D2 after N1-l-N2-i- N11 characters plus a time interval of T2 milliseconds will be RznTz/Tl-(N1-l-N2-l- Nn)(T1--T2)/T1 parts of a revolution. In each instance When Xn becomes zero, the distributors are again in phase with each other and the cycle repeats. It will be noted that the maximum difference of space phase between distributors D2 and D1 will be Q-|R=T2/ T1 parts of a revolution.

Since each storage relay 21 through 25 and 81 through stores each intelligence baud for 2T2 vmilliseconds, and since the greatest time phase difference between distributors D2 and D1 is (Q-l-R)T1=T2 milliseconds there is provided an excess of storage capacity of 2T2-T2=T2 milliseconds which may be best utilized by selecting a starting (or reference) phase relationship such that when clutch 17 engages at the start of the first character of the first sequence of characters, distributor D1 is in such position as to close contact Z3. The starting phase used in the detailed description of the preceding paragraphs was selected solely for great er clarity of explanation.

The differential gear assembly 47 is driven simultaneously by shafts 19 and 37 in such a manner that a gain of one revolution of shaft 19 with respect to shaft 37 will, through the operation of gears 45 and 46, revolve cam 43 (see Fig. 3 section B-B) through 180 arc degrees in the direction indicated by the arrow labeled ADV.

The maximum value of Q, that is, the maximum amount by which distributor D2 can lead distributor D1 is Tz/ T1 parts of a revolution. In consequence, the maximum advance of cam 43 is (180 T 2)/T 1 degrees from the initial position depicted in Fig. 3. The maximum value R, that is, the maximum amount by which distributor D1 can lead distributor D2 is (T1-T2)T1 parts of a revolution. In consequence, the maximum retardation of cam 43 is 180(T1T2)T1 degrees from the initial position depicted in Fig. 3. The minimum value of Q, that is, the minimum amount by which distributor D2 can lead distributor D1 at the end of a sequence of characters is (2T2-T1)/ T1 parts of a revolution. In consequence, the minimum advance of cam 43 is l80(2T2-T1)/T1 degrees from the initial position depicted in Fig. 3. The minimum value R, that is, the minimum amount by which distributor D1 can lead distributor D2 is zero. In consequence, during each sequence of input characters, cam 43 will advance from the initial position depicted in Fig. 3 a minimum of l80(2T2-T1)/T1 degrees and a maximum of T2)/T1 degrees. A difference of l80(T1-T2)/T1 degrees exists between these limits. In similar con sequence, at the end of the marking-stop signal which concludes each sequence of input characters, the cam 43 will retard beyond the initial position depicted in Fig. 3 a minimum of zero degrees and a maximum of 180(T1-T2)/T1 degrees; the sameA difference of 180(T1-T2)/T1 degrees exists between these limits as 7 between the limits to which cam t3 advances. The arc of motion of cam 43 is always (lSO T2)/ T1 degrees but the limits of this motion rhythmically increase and decrease by l80(T1-T2)/T1 degrees.

The magnet of relay Sii is energized on aiternate halfcycles of an alternating current the frequency of which is synchronous with a multiple of the speed of the receiving PTA; the synchronous receiving PTA is normally designed to provide such current. Resistor S6, having a resistance approximately equal to that of the magnet of relay t), is provided to equalize the load on the source of synchronous frequency during alternate half-cycles; the distribution between magnet and resistor is controlled by the rectihers 54% and 55.

In consequence of the foregoing, tongue 56A of relay Sti engages spring 56C and then spring 53B on alternate half cycles of the current which is synchronous with a multiple of the speed of the receiving PTA. A land encompassing one-half of the periphery of cani 52 causes tongue SA of switch 5i to engage spring 531C and then spring 51B on alternate half revolutions of shaft 58 which is driven by motor M1. Switch 5i is positioned with respect to cam 52 so that, under ncrmal synchronous operating conditions, the time phases of alternation of tongues SlA and 53A are in quadrature and so that a tendency of tongue SlA to lag this quadrature phase position will decrease the interval dur,- ing which both tongues engage springs SilB and 59C respectively, thus decreasing the ield current and increasing the speed of motor M1; and, conversely, so that a tendency of motor M1 to speed up will increase the aforesaid interval, increase the field current and reduce the speed of motor M1. In this manner, shaft 53 is caused to rotate in synchrony with a current which is synchronous with a multiple of the speed of the receiving PTA. The gear ratio of reduction gear 36 is chosen to make the rotation of shaft 37 and of distributor D1 synchronous with the speed of the receiving PTA.

Switches F1 and F2 (Fig. 3 section B-B) are positioned so that the land of cam 43 does not close them as it oscillates between maximum limits. Whenever the speed of the receiving PTA becomes slightly less than the speed of the transmitting PTA, the maximum limits of oscillation of cam 43 will tend to advance in the direction depicted by the ADV arrow in Pig. 3 and once during each Oscillation the land of cam 43 will close switch F1 which energizes a circuit normally provided in the synchronous receiving PTA for the purpose of increasing the speed of the receiving PTA; this increases the s eed of distributor D1 in the manner reviouslv described, thus retarding the limits of oscillation of cam 43 to the extent that switch F1 is no longer pulsed, thus allowing the receiving PTA to run at the newly corrected speed.

Whenever the speed of the receiving PTA becomes slightly greater than the speed of the transmitting PTA, the limits of motion of cam t3 will retard and, once during each oscillation, the land of cam 43 will close switch F2 which energizes a circuit normally provided in the synchronous receiving PTA for the purpose of decreasing the speed of the receiving PTA. A reduction of speed of the receiving PTA reduces the rate of relay 5t) and the rate of distributor Dr in the manner previously described. A reduction in the speed of distributor D1 advances the limits of oscillation of cam 43 to the extent that switch F2 is no longer pulsed, thus allowing the receiving PTA to run at the newly corrected speed.

Noise or fading on the rnux circuit may delete one or more time differential blanks thus causing the receiving mux to substitute a start baud at the beginning of the period T2 milliseconds long when there should have been a marking-stop signal. As previously demonstrated, at the instant To that the T2 millisecond marking-stop baud is due to be received, the land of cam 43 will have advanced to a position of either; Case l: 180 T2/ T1 degrees or, Case 2: 180(2T2T1)/Tr degrees from the initial position shown in Fig. 3. Upon receipt of an accidental spacing-start baud instead of a T2 millisecond marking-stop baud, in case l cam 43 will advance by 180(T1-T2)/T1 degrees and at the time Tu-l-Tz will reach a position 180 degrees advanced from the position shown in Fig. 3, whereupon the then leading edge of the land of cam 43 closes switch F3 which connects positive battery to the magnet of relay 61 through normally closed contacts 60e and 6th of relay 6G, thus closing contacts 61a and 6h, through which positive battery is connected to the magnet of relay 61 through resistor Ris thus holding relay 61 energized even after switch F3 has opened. (Note that switch F7 is open because at this moment the land of cam 43 has advanced to the vicinity of switch F3.) Switch F3 energizes relay 61 at time T (wl-T 2 and opens normallyclosed contacts 6i@ and old thus opening the circuit from positive battery through contacts 60e and 60d of relay 6@ to terminal T, thus preventing clutch magnet 9 from engaging clutch 1'7 upon receipt of the start baud, or any other baud of the character starting at time To-l-Tz. Since distributor D2 is thus constrained from rotating, the continuing rotation of distributor D1 will retard the land of cam 43 by 180 T2/ T 1 degrees from its position at time To-l-T 2 to a new position of degrees at time To-l-ZTz whereupon the land of cam 43 closes switch F7 thus shortcircuiting the magnet of relay 61; (and harmlessly, resistor R16) thus opening contacts 612. and 61h whereby relay 61 remains de-energized thus closing contacts 61e and 61d and restoring positive battery to terminal T whereby clutch 17 is permitted to engage upon receipt of the start-baud due at time To-l-ZT 2. Had the T2 millisecond stop-baud which was due at time To not been accidentally changed to a start-baud, distributor D2 would not have rotated during the period commencing at time To and at time T o-i-T 2 the land of cam i3 would have been retarded by 180 T2/ T 1 degrees from its position of T2/ T 1 degrees and would have reached a position of zero degrees from the position shown in Fig. 3. During the receipt of the rst character of the next sequence of characters cam 43 would have advanced by 180(T1T2)/T1 degrees, and at time T0-}-2T2 would have arrived at a new position of 180(T i-T 2)/ T1 degrees. This is the same position that cam 43 reached at time To-I-ZT 2 through the action of switch F3.

In case 2 mentioned above, cam 43 had advanced to a position of l8O(2T2-T 1)/ T1 degrees at time To when the marking-stop baud was accidentally changed to a start-baud. This start-baud and the start-baud of the next succeeding character will advance cam 43 by 2( 180) (T1-T2)/T1 degrees to a new position of degrees at time T o-l-2T2, whereupon switch F3 in the manner described, prevents rotation of distributor D2 upon receipt of the next start-baud and cam 43 retards by 180 T2/ T1 degrees to a new position of 180 T2/T1 degrees from its position of l80(2T2-T1) T1 degrees to a new position of degrees at time Tn-l-Tz. The start-bauds of the next succeeding two characters would have resulted in the advancement of cam 43 by 2(180) (T1-T2)/T1 degrees to avanao 9 a new position of 180( T1-T2)/ T1 degrees at time To-i-3 T2. This is the same position that cam 43 reached through the action of switch Fs.

The foregoing detailed description of case 1 and case 2 demonstrates that whenever noise or fading on the mux circuit transforms a speed-differential blank into some garbled character, the action of the switch F3 in concert with the inherent speed stability of the mux and of the receiving PTA, will maintain the proper phase relationship of distributors Di and D2 and assure that cam 43 resumes its oscillations within the normal arc of motion within a time interval of two, or at the most three, multiplex character intervals.

Noise or fading on the mux circuit may delete one or more spacing-start bauds from the output of the mux and consequently from the line input relay 2. The design of the AN/FGC-S is such that when a spacing-start baud is not present at the beginning of an output character, a marking-stop baud is delivered for the entire T2 millisecond character interval.

Assume that cam 43 has advanced, at time To, by N(l80)(T1-T2)/ T1 degrees from the position shown in Fig. 3. Also assume that noise or fading on the mux circuit transforms the start-baud due at time To into a T2 millisecond stop-signal. In consequence, cam 43 instead of advancing another 180(T1-T 2)/ T1 degrees, will retard by 180 T 2/ T1 degrees and, at time To-I-Tz, will assume a new position of N(l80) (T1-T2)/T1-180 Tz/Ti degrees. if N(180)(T1-T2)/T1 equals the maximum advance of cam 43, namely, 180 T 2/ T1 degrees, a marking-stop baud was normally due at time To and the situation is unchanged. If N(l80) (T1-T2) /T1 Aequals the minimum advance of cam 43, namely, l80(2T2-T1)/ T1 and a marking-stop baud was due at time To, the situation remains unchanged but; Case 3: If N(180)(T1-T2)/T1 equals 18O(2T2-T1)/T1 and a marking-stop baud not due at time To is accidentally received, cam 43 will retard and assume a new position of at time T o-I-Tz at which time a marking-stop signal will be due and the receipt thereof further retards cam 43 by 180 Tz/ T1 degrees to a new position of at the time Tu-l-2T2. In thus retarding, cam 43 closed switch F4 which latches-up relay 60 in the manner previously described in connection with relay 61. The latching-up of relay 60 opens contacts 60C and 60d thus removing positive battery from terminal T and preventing the next spacing-start baud (due at time To-l-ZTz) from engaging clutch 17. The latching-up of relay 60 also opens contacts 60e and 601 thus disabling switch F3. (Note that switch Fa is open during the preceding operation.) In consequence of the continued disengagement of clutch 17, cam 43 continues to retard another 180 T 2/ T 1 degrees and at time Tu-ll-3T2 reaches position -]l80(T1-Tz)/T1 degrees from the position shown in Fig. 3. During this further retardation, cam 43 closes switch Fa thus releasing relay 60 and permitting the start-baud of the next character to cause the engagement of clutch 17. The releasing of relay 60 also closes contacts 60e and 601 thus restoring the action of switch F3. In this case 3, had the start-baud not been omitted at the time To, cam 43 would have advanced from position 180(2T z-T1)/T1 degrees by l80(T1-T2)/ T1 degrees and would have reached position 180 T2/ T 1 degrees at time T n-l-T 2 when the arrival of the expected marking-stop signal would have retarded cam 43 by 180 Tz/ T1 degrees to zero degrees (reference position) at time T o-l-ZTz. Receipt of the next character would have advanced cam 43 to position l80(T1-T2)/ T1 degrees at time To-l-3T2. This is the same position that cam 43 reached through the action of switch F4.

10 Case 4; 1f N(1so)(T1-T2)/T1 is less than the minimum advance of cam 43, namely less than (2Tz-T1)/T1 degrees at time To when a start-baud is accidentally changed into a marking-stop signal, cam 43 will retard 180 T 2/ T1 degrees and at time To-l-T 2 will reach a (retard) position 2(180) (T1-T2)/T1 degrees, or more, thus closing switch F4 which, as previously described, latches-up relay 60, prevents clutch 17 from engaging, and disables the function of switch F3. Since clutch 17 cannot engage, cam 43 retards another 180 T 2/ T1 degrees and at time To-l-ZTz reaches a position relative to the position shown in Fig. 3 of measured in an advancing direction. If the start baud at time To had not been accidentally changed into a markingstop baud, cam 43 would have advanced by 2(180) (T1-T2)/T1 degrees during the receipt of the next two characters and would have reached position -|-(N-|2) (180) (T1-T2)/T1 degrees at time T o-l-ZT 2. This is the same position reached by cam 43 due to the action of switch F4.

The foregoing detailed description of case 3 and case 4 demonstrates that whenever noise or fading on the mux circuit transforms a spacing-start baud into a markingstop signal, the action of switch F4 in concert with the inherent speed stability of the mux and of the receiving PTA, will maintain the proper phase relationship of distributors D1 and D2 and assure that cam 43 resumes its oscillations within the normal arc of motion within a time interval of two, or at the most three, mux character intervals.

The retardation of cam 43 through 2(180)T2/ T1 degrees as the result of an accidentally omitted start-baud, results in the momentary closure of switch F2 which applies a slight slow-down speed correction to the synchronous receiving PTA, followed by the momentary closure of switch F1 which applies a slight speed-up speed correction to the lreceiving PTA. These two successive corrections substantially neutralize each other. The speed correction accomplished by one closure of switches F1 or F2 may be very slight because the time interval T1 in the transmitting and receiving PTA, and the time interval T2 in the mux is held very nearly constant by oscillators of extremely constant frequency. The speed of the receiving PTA is changed appreciably only by repeated successive closures of switch F1 or of switch F2.

Because of the inherent tendency of cam 43 and its associated switches to maintain a iixed average phase relatonship between distributors D1 and D2 despite the effects of noise and fading on the mux circuit, the printing telegraph signal normalizer cannot seek-out the correct initial starting phase relationship; this must be accomplished at the commencement of operations by manually changing the phase of distributor D1 (by adjusting the arc position of switch 51) until cam 43 oscillates normally without closing switches F1 through F4.

The'invention described in the foregoing, one embodiment of which is illustrated in Figs. 1, 2 and 3, will also operate to convert 7.42 unit printing telegraph signals to 7.0 unit characters suitable for controlling a synchronous receiving PTA, Whenever said characters which are originated by a 7.0 unit transmitting PTA have been converted to 7.42 unit characters through the action of standard regenerative-repeaters which may be included in the communication link. In the circumstances stated above, the start-stop regenerative-repeaters receive the 7.0 unit synchronous PTA transmission as if it were a biased 7.42 unit start-stop transmission and they regenerate and amplify the signal into a standard 7.42 unit start-stop transmission which the receiving 7.0 unit synchronous PTA can neither translate nor synchronize to.

If the duration of` each character emitted by the transmitting synchronous PTA is T1 milliseconds divided into seven equal time intervals, the duration of each character emitted by the regenerative-repeater will be T1 milliseconds divided into six equal but shorter time intervals followed by a seventh time interval 1.42 times longer than the preceding six. When the 7.42 unit signals are applied to the input line relay 2 of Fig. 1, the functioning of my invention is substantially the same as previously described except that the advance and retardation of cam 43k is much slower than that previously described and results only from slow drifting speed differencesv between the synchronous transmitting and receiving PTA. Distributor D2 distributes the` 7.42' unit incoming signals to the storage relays and distributor D1 reads-out the information stored in the storage relays and delivers it to output line relay 9G in the form of 7.0 unit printing telegraph signals which may be translated by the receiving synchronous PTA. The switches associated with cam 43 will then operate in the manner previously described to correct the speed of the receiving synchronous PTA and to correctfor the otherwise deleterious effects of characters omitted or added in the communications link as the result of noise or fading on that link.

Distributor D1 may be designed to deliver to line output relay 90 either 7.0 unit or 7.42 unit printing telegraph signals as desired.

Figs. l, 2 and 3 have been used solely for illustrative purposes. There are many possible variations of the individual circuits and components that may be utilized to practice my invention. ln particular it is noted that all of the functions performed by the distributors, storage relays (storage cells), cams (timers) and switches, are achievable through the use of electron-tube circuits, transistor circuits, bi-stable magnetic circuits, and other electronic devices all of which are well known to those skilled in the art.

I claim:

l. A printing telegraph signal normalizer device cornprising an input circuit for receiving intermittent startstop printing telegraph signals wherein each received character is represented by a group of signals or bauds comprising a start baud followed by a group of intelligence bauds followed by a stop baud, a first signal distributor operated synchronously with said received characters for distributing the said intelligence bauds included therein to storage cells, a first group of storage cells for storing said received intelligence bauds of alternate received characters, a second group of storage cells for storing said received intelligence bauds of alternate characters not stored in said first group of storage cells, a first switch for switching the intelligence bauds of alternate received characters into said first group and into said second group of storage cells alternately, a second signal distributor operated synchronously with a synchronous receiving printing telegraph apparatus for sampling the intelligence bauds stored in said first and said second groups of storage cells, a second switch for switching to said second signal distributor in an alternate character manner the intelligence bauds stored in said first group and in said second group of storage cells, an output circuit for delivering signals representing output characters to said synchronous receiving printing telegraph apparatus wherein each output character includes intelligence bauds sampled by said second signal distributor, a differential circuit for comparing the signal distribution rate of said second signal distributor with the average signal distribution rate of said first signal distributor, said differential circuit including a first group of rate-correction circuits for correcting the rate of said second signal distributor and its synchronously operated printing telegraph apparatus to equality with the average rate of said first signal distributor whenever said input circuit is receiving normally intermittent start- 12 stop signals, saiddifferential circuit also including a second` group of rate-correction circuits for correcting the effective average rate of said first signal distributor to equality with the rate of said second signal distributor during periods when said input circuit is receiving abnormally intermittent start-stop signals.

2. The device of claim l wherein the said input circuit comprises, a relay which connects battery or ground potential in accordance with the varying potential of the received signal to the common distributor contacts of saidfirst distributor and to an auxiliary relay which actuates a magnet-operated clutch whereby said first distributor is caused to stop or to distribute the bauds of a receivedcharacter in synchrony with the rate at which said bauds are received, said first distributor comprising a plurality of cams and associated distributor contacts which contacts are normally open but are momentarily closedl in sequence during acomplete rotation of said cams, said cams being rotated by av motor whenever said o clutch is engaged.

3. The device of claim l wherein the said first group and the said second group of storage cells comprises a groupA of electromagnetic relays provided with auxiliary contacts whereby said relays remain energized after having been energized by external means and whereby said relays remain de-energized after having been de-energized by external means.

l4. The device of claim l wherein the said first switch for switching the intelligence bauds comprises a multipole double throw relay actuated by contacts associated with a cam, said cam being geared to said first signaldistributor.

5. The device of claim l wherein the said second switch for switching intelligence bauds to said second signal distributor comprises a multi-pole double throw relay actuated by contacts associated with a cam, said cam being geared to said second signal distributor.

6. The device of claim l wherein the said second signal distributor comprises a plurality of cams and associated distributor contacts which contacts are normally open but are momentarily closed in sequence during a complete rotation of said cams, said cams being rotated by a motor in synchronism with the said receiving synchronous printing telegraph apparatus.

7. The device of claim l wherein the said output circuit comprises a relay actuated by signals distributed thereto by the said second signal distributor.

8. The device of claim 1 wherein the said differential circuit for comparing the distribution rates of said first and said second signal distributors comprises a mechanical differential driven simultaneously by extension-shafts from both said signal distributors, and wherein the said differential rotates a cam an amount proportional to the difference of the time integrals of the rates of said first and said second distributors, and wherein the said cam actuates switches constituting said first group and said second group of rate-correction circuits.

9. A printing telegraph signal normalizer device comprising an input circuit for receiving start-stop printing telegraph signals representing received characters, a plurality of storage cells, a first signal distributor operated synchronously with said received characters for distributing the intelligence bauds of said received characters to said storage cells, a second signal distributor operated synchronously with a synchronous receiving printing telegraph apparatus for sampling the intelligence bauds stored in said storage cells, an output circuit for delivering signals representing output characters to said synchronous receiving printing telegraph apparatus wherein each output character includes intelligence bauds sampled from said storage cells by said second signal distributor, and a differential means for comparing the signal distribution rate of said second signal distributor with the distribution rate of said first signal distributor, said differential means including means for correcting the rate of said second signal distributor and its synchronously operated printing telegraph apparatus to equality with the average rate of said rst signal distributor Whenever said input circuit is receiving undisturbed start-stop signals, said differential means also including means for correcting the effective average rate of said first signal distributor to equality with the rate of said second signal distributor Whenever said input circuit is receiving disturbed signals.

References Cited in the tile of this patent UNITED STATES PATENTS 

